Paving machines are well known in the art which apply paving mixtures, such as a hot asphaltic bituminous concrete paving material, to the surface of the roadway. Self-propelled machines of this type typically have hopper at the front of the machine, a conveyor which extends from the hopper to the rear of the machine, and apparatus at the discharge end of the conveyor for spreading and smoothing the paving material onto the roadbed, which apparatus may include spreading screws in the form of transversely extending left and right augers which distribute the paving material, and a finishing screed at the rear of the machine for smoothing the spread paving material.
It is recognized, for example in U.S. Pat. Nos. 5,069,578 and 5,279,500, that may be desirable to apply a liquid binding material to the surface of a clean dry roadway. According to these patents the liquid binding material is applied at a location behind the propulsion means of the self-propelled machine and in front of the spreading screws and the smoothing table or screed. In U.S. Pat. No. 5,069,578 conveying means are disclosed which are of the drag slat type, the conveyor having upper and lower flights. The upper flight conveys the material to the rear of the machine. This form of conveyor has a disadvantage in that some of the paving material will adhere to the slats past the point where it is supposed to be discharged. This material is then carried back by the lower flight and may then drop either onto the surface of the roadway, or alternatively build up on the floor of the chassis of the self-propelled machine. It is undesirable that this material fall on the roadway because its presence on the roadway will prevent the application of liquid binding material to the roadway where there is already new, loose, extraneous paving material on the roadway.
The Vogele Super 1800 SF road paver is similar to U.S. Pat. No. 5,069,578 in that it discloses a paver having a spray assembly for spraying a bitumen emulsion just before the asphaltic paving material is placed on the surface of the roadbed. This paver includes a self propelled crawler unit having a hopper at the front, a spray bar to the rear of the crawler tracks, a pair of augers (or worm conveyors) which convey the material from the hopper to a location above and beyond the spray bar, spreading screws for spreading the delivered material, and a screed behind the spreading screws. The crawler chassis also supports an emulsion tank and an operator's station. It is an advertising feature of this machine that worm conveyors are provided to deliver the material from the feed hoppers to the transverse spreading screws, the product literature stating that "This modified conveyor system ensures that no paving material can drop onto the base not yet sprayed with emulsion." The Super 1800 SF road paver is designed for use with hot asphaltic bituminous concrete paving material. To this end the troughs beneath the worm conveyors are heated electrically to insure that if there is a work stoppage the material within the troughs will not cool down to such an extent that it would impede rotation of the worm conveyors. While the Vogele Super 1800 SF road paver performs in a satisfactory manner in many circumstances, particularly for narrow twisting roadways, it has significant disadvantages. Thus, the worm conveyors are open at the top. This will permit heat to escape, causing potential cool down problems to the hot mix. In addition, the crawler suspension system is not desirable in many applications since it limits the size of the machine to relatively small throughput. Also, the emulsion tank is relatively small.